Diesel vehicles tend to be increasingly sold due to excellent energy efficiency and power. However, the diesel vehicles exhaust larger amounts of particulate matters (PM) and nitrogen oxides (NOx) as compared to gasoline vehicles and are a cause of the pollution in a metropolis. In particular, a regulation for the nitrogen oxides that causes ill and environmental pollution has been strengthened more and more and there has been tried many efforts to develop a technologies for removal thereof.
As the most effective method for the removing the nitrogen oxides, a selective catalytic reduction (SCR) is come into a spotlight, in which various reducing agents and catalysts can be employed according to various conditions such as properties of the applied process, environmental aspects and economics. Since a selective catalytic reduction by ammonia (NH3/SCR), which is most effective for removing the nitrogen oxides in a stationary source such as a power plant and an incinerator and is being commercially used, has a problem resulted from store/transportation and use of the ammonia, urea which can be cracked to produce the ammonia is used for the removing the nitrogen oxides in the exhaust gas from the vehicles. The method for using the urea as a reducing agent is studied recently and largely for a post-treatment apparatus in diesel vehicles, and is actually commercialized in Europe.
However, one important problem in application of this technology into vehicles is a carrier used in a catalytic converter capable of carrying the catalyst. A ceramic cordierite carrier developed by Corning in 1975 is now used by at least 95% in the catalytic converter for the vehicles across the world. However, lighter frame and parts for the vehicle are required in an aspect of fuel efficiency and the weight of the cordierite carrier used as the catalyst carrier can also be a problem. To challenge this problem, lighter material of a noble concept has been studied.
Korean patent published application Nos. 10-2007-0013206 and 10-2007-0012243 disclose methods of fabricating a ceramic fiber filter for use as a diesel particulate filter for removing particulate matters exhausted from the diesel vehicles, and the ceramic fiber filter is expected to be very useful since it has a high porosity (at least 80%), is resistive to heat and impact due to unique elasticity of the fiber and can be formed into various shapes. Therefore, it is important to study whether technical development of the catalyst carrier using the ceramic fiber can replace the existing cordierite carrier or not.
Further, the object of the present invention is to develop a catalyst for removing the nitrogen oxides and a carrier for the same, with an excellent stability, which not only have a high initial efficiency of NOx removal but also can maintain the initial activity even after a long term operation under humid environment.